The Invisibility Watch, also known as the Invis Watch, is the default PDA weapon for the Spy. It is a piece of advanced technology embodied in a digital watch with a partially wooden face and a silver segmented wristband.

Using the alternate fire button with any other weapon equipped will allow the player to Cloak, blending in perfectly with his surroundings and effectively becoming invisible, allowing them to infiltrate enemy territory and stalk targets without being seen. The Spy cannot attack while cloaked but will still be able to use his Disguise Kit. It takes around 1 second to fully Cloak, during which Cloak energy is already consumed. Decloaking requires the Spy to wait approximately 2 seconds for the process to be complete.

While cloaked, the Spy receives 20% less damage from all sources. In addition, while the Spy is invisible, status effects (eg: Jarate, bleed, afterburn) will have reduced duration. If the Spy takes any damage while cloaked, or bumps into an enemy player, then his cloak will momentarily 'flicker' and be visible to enemy players.

The Cloak generated by the Watch has a limited duration, indicated by a bar on the HUD as well as a glowing bar meter on the watch face itself. The Cloak meter will automatically recharge when not in use. Resupply areas, Dispensers, and ammo can also replenish the Cloak meter, even when cloaked. A large ammo box will fully recharge the Cloak, medium boxes will restore 50%, small boxes will restore 20%, while medium ammo boxes dropped by players and building pieces will both restore 25%. Dispensers, even those of the opposite team, can maintain Cloak energy to keep the Spy cloaked, indefinitely. While a level 1 Dispenser simply stops the watch from losing energy while cloaked, level 2 and 3 actually recharge it slowly. Additionally, scoring a hit with the L'Etranger will replenish 15% Cloak, and successfully killing an enemy with the Big Earner will replenish 30%.

While cloaked, allies can still see the Spy in the form of a translucent outline.